The present invention relates generally to the field of fire and smoke dampers, and more particularly to the field of fire and smoke dampers which must be held in a preselected position under fire conditions.
In the past, it has been known to close fire dampers and/or to open smoke dampers under fire conditions either in response to heat or, alternatively, in response to a signal received from a remote source.
Heretofore, such fire and/or smoke dampers have generally been held in place by springs, or other operating means which exert influences on the dampers throughout their normal operating ranges, but which, as in the case of springs attached to the blades, are allowed to overcome whatever means normally counteracts those forces but which, under fire conditions are released. For example, in a folding blade fire damper, the damper blades may be held in the open position by a cable attached to a fusible link. Either gravity, springs or some other means may be employed to tend to force those blades towards the closed position. Upon fire conditions, when the fuseable link melts, the forces resisting closure of the blades are eliminated and the blades are forced into the closed position.
While the above-described arrangement for causing the closure (or alternatively, the opening) of dampers is suitable for many purposes, in the event that the damper is also to be used as a volume control damper, such arrangements suffer from the disadvantage that the damper operating mechanism must routinely overcome either opening or closing forces during the routine operation of the damper, when in fact the forces applied to the damper blades may only be needed to maintain the blades in one of those positions under fire conditions.